Chemical circulation system and methods of cleaning chemicals

ABSTRACT

A method includes passing a chemical solution through a metal-ion absorber, wherein metal ions in the metal-ion absorber are trapped by the metal-ion absorber. The chemical solution exiting out of the metal-ion absorber is then used to etch a metal-containing region, wherein the metal-containing region includes a metal that is of a same element type as the metal ions.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/050,014, entitled “Chemical Circulation System and Methods ofCleaning Chemicals,” filed on Oct. 9, 2013, which application isincorporated herein by reference.

BACKGROUND

Wet etching is a commonly used method in the manufacturing of integratedcircuits. For example, in damascene processes, titanium nitride iscommonly used to form hard masks, which are used to define the patternsof trenches and via openings, in which copper is filled to form metallines and vias. Hence, hard masks need to be patterned first, so thattheir patterns may be transferred to the underlying dielectric layers.Traditionally, after the formation of the metal lines and vias, the hardmasks are removed by a Chemical Mechanical Polish (CMP) process.

The removal of titanium nitride may be performed using a wet etch (wetclean) process, during which a chemical solution is used to etch thetitanium nitride (TiN). Conventionally, there were two types ofwet-clean circulation system. The first is known as the drain-modesystem. In the drain-mode system, the wet-clean chemical is pumped intoa tank for storage. From the storage, the wet-clean chemical is passedthrough a particle-filter for filtering large particles. The wet-cleanchemical is then heated, and then sent to a process chamber, in whichwafers are sprayed with the wet-clean chemical in order to remove thehard mask. The drain-mode wet-clean circulation system results in morewaste since the wet-clean chemical is not reused. The manufacturing costis also high due to the cost of the wet-clean chemical.

The second type of wet-clean circulation system is known as thecirculation-mode system. In the circulation-mode system, the wet-cleanchemical is pumped into a tank for storage. From the storage, thewet-clean chemical is passed through a particle-filter for filteringlarge particles. The wet-clean chemical is then heated, and thenconducted to a process chamber, in which wafers are sprayed with thewet-clean chemical in order to remove the hard mask. The sprayedwet-clean chemical, which has been used, is then collected, and pumpedback to the storage, so that it can be filtered, heated, and sent backto the process chamber again. By using the circulation-mode wet-cleancirculation system, the waste of the wet-clean chemical is reduced.However, the dissolved titanium ions remain in the wet-clean chemical,and remain in the circulation system and the pipelines. With theincrease in the amount of titanium ions in the wet-clean chemical, theclean efficiency and the TiN removal rate in the wet clean process arereduced. Furthermore, due to the variation in the amount of titaniumions in the wet-clean chemical, the efficiency in the removal of thetitanium nitride has variations accordingly, causing variations in theresulting hard mask clean and removal process.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a circulation-mode wet-clean circulation system inaccordance with some embodiments;

FIG. 2 illustrates a porous exchanger in accordance with someembodiments, wherein the porous exchanger is disposed in a metal-ionabsorber in the circulation-mode wet-clean circulation system;

FIG. 3 illustrates an exemplary process for rejuvenizing the porousexchanger in accordance with some embodiments; and

FIG. 4 illustrates an exemplary process for rejuvenizing the porousexchanger in a first channel of a dual-channel metal-ion absorber inaccordance with some embodiments; and

FIG. 5 illustrates an exemplary process for rejuvenizing the porousexchanger in a second channel of the dual-channel metal-ion absorber inaccordance with some embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable concepts that can be embodied in a wide varietyof specific contexts. The specific embodiments discussed areillustrative, and do not limit the scope of the disclosure.

A method for absorbing metal ions in wet-etch chemicals and theapparatus for performing the same are provided in accordance withvarious exemplary embodiments. The intermediate stages of absorbing themetal ions are illustrated. The variations of the embodiments arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIG. 1 illustrates circulation-mode wet-clean circulation system 10,which is configured to absorb metal ions in wet-clean chemical 18, whichis a chemical solution. Wet-clean circulation system 10 includes pump12, which functions to pump wet-clean chemical 18 to storage 16. In someembodiment, wet-clean chemical includes polyethylene-polypropyleneglycol, glycolether compound, modified oxirane polymer (such asmethyl-), organosulfur compound, methylimidazole, aminoethanol,aminopropanol, hydroxyamine, tetramethylammonium hydroxide, hydrophobicor hydrophilic surfactant, hydrogen peroxide, or combinations thereof.Pipes are used to connect the components shown in FIG. 1, whereinreference numeral 19 represents the pipes for conducting wet-cleanchemical 18.

Pump 12 may receive from inlet 14 unused wet-clean chemical 18.Throughout the description, the wet-clean chemical 18 may be referred towith a letter such as “A,” “B,” and “C” suffixed to the referencenumeral 18, so that wet-clean chemical 18 in different stages ofwet-clean circulation system 10 may be distinguished from each other.Wet-clean chemical 18 is stored in storage 16 before it is used.

Filter 20 is connected to storage 16 to receive wet-clean chemical 18.Filter 20 is configured to filter the particles in wet-clean chemical18. In some embodiments, filter 20 is configured to filter the particlesthat are larger than about 15 nm, while the particles that are smallerthan about 15 nm are not filtered. Hence, after passing filter 20,wet-clean chemical 18 may still include the particles that have sizessmaller than about 15 nm. Furthermore, metal ions have size smaller thanabout 15 nm, and hence are not filtered by filter 20.

Metal-ion absorber 22 is connected to filter 20 in order to receive thewet-clean chemical 18 that have been filtered by filter 20. FIG. 2schematically illustrates porous exchanger 24, which is a part ofmetal-ion absorber 22. The casing outside of the illustrated porousexchanger 24 is not illustrated. Porous exchanger 24 has the function oftrapping the metal ions in wet-clean chemical 18 when wet-clean chemical18 penetrates through the pores of porous exchanger 24. In someembodiments, porous exchanger 24 is a film, as illustrated in FIG. 2.

In some embodiments, porous exchanger 24 includes surface 24A facing theincoming wet-clean chemical 18A, which penetrates through the pores inporous exchanger 24, and exits out of porous exchanger 24 from surface24B. The exiting wet-clean chemical 18 is denoted as 18B to indicatethat the metal ions in wet-clean chemical 18A have been trapped byporous exchanger 24. In accordance with some embodiments, thickness T ofporous exchanger 24 is in the range between about 0.0001 mm and about 10mm. It is appreciated, however, that the values recited throughout thedescriptions are merely examples, and may be changed to differentvalues.

In accordance with some embodiments, porous exchanger 24 includes a basematerial that is porous and includes many micro-pores, which areinterconnected to extend from surface 24A to surface 24B. In accordancewith some embodiment, the base material includes porous ceramic. Inalternative embodiments, the base material includes a carbon-containingor a silica-containing material that is porous. The base material thushas a structure similar to a sponge. The porosity of the base materialmay be in the range between about 10 percent and about 60 percent.Accordingly, the surfaces of the base material, which surfaces includesthe inner surfaces in the pores, are much larger than the surface ofporous exchanger 24 facing wet-clean chemical 18.

The surfaces of porous exchanger 24 are coated with a polymer, which maybe a resin. The polymer is coated into the pores, so that the surface ofthe polymer that may contact wet-clean chemical 18 is significantlyincreased. The polymer has the function of trapping the metal ions,which may include titanium, copper, cobalt, or the like. Depending onthe metal ions that are to be absorbed, the polymer may be selecteddifferently. In the exemplary embodiments in which titanium ions presentin wet-chemical 18A, the polymer includes functional groups such ascation (R—H), anion (R—OH), amphoteric (R—H+R—OH), or the like. Theexemplary polymer includes cross-linked polystyrene, modified zeolite,colestipol, cholestyramine, epoxy, or the like. Porous exchanger 24 mayalso include activated carbon coated on the base material.

Porous exchanger 24 traps the metal ions, and hence removes the metalions from wet-clean chemical 18A when it passes through porous exchanger24. Equations 1, 2, and 3 illustrate some exemplary chemical reactionsfor trapping the metal ions:R—H+M²⁺→R-M+2H⁺  [Eq. 1]R—H+M³⁺→R-M+3H⁺  [Eq. 2]R—H+M⁴⁺→R-M+4H⁺  [Eq. 3]Wherein M²⁺ represents divalent metal ions such as copper ions andtitanium ions, M³⁺ represents trivalent metals such as aluminum ions andtitanium ions, and M⁴⁺ represents tetravalent metal ions. R representsthe function groups in the polymer. The metal ions react with thepolymer to form the R-M (with M being the metal), and hence the metalions are trapped.

The resulting wet-clean chemical 18B (FIGS. 1 and 2) has much less metalions than in wet-clean chemical 18A. In some embodiments, the metal ionconcentration in wet-clean chemical 18B is less than about 0.1 percentthe metal ion concentration in wet-clean chemical 18A. Furthermore, themetal ion concentration in wet-clean chemical 18B may be lower thanabout 1000 ppm in accordance with some embodiments.

Referring back to FIG. 1, the metal ion concentration in wet-cleanchemical 18B is monitored by monitor 26, which performs in-linemonitoring when wet-clean chemical 18B passes through. The monitoringmethod may include Fourier Transform Infrared (FTIR) spectroscopy,Ultra-Violet (UV) visible spectroscopy, Near Infrared (NIR)spectroscopy, or the like. It is appreciated that with the increase inthe trapped metal ions in porous exchanger 24, porous exchanger 24'sability for trapping metal ions reduces. Therefore, it needs to bedetermined when porous exchanger 24 needs to be replaced or rejuvenized,or when the wet-clean chemical 18 needs to be replaced.

Next, as also shown in FIG. 1, wet-clean chemical 18B is heated byheater 28, for example, to a temperature between about 30° C. and about65° C. The heated wet-clean chemical 18B is then supplied to processchamber 30, in which a process is performed on wafer 32. In someembodiments, the process includes removing a metal containing regionthat contains the same type of metal that is trapped by metal-ionabsorber 22. In some exemplary embodiments, wafer 32 includes a hardmask that includes titanium nitride.

An exemplary process that involves the using of circulation-modewet-clean circulation system 10 is briefly described below. It isappreciated, however, that circulation-mode wet-clean circulation system10 may also be used in other processes other than described. Theexemplary process includes forming a metal hard mask (not shown) overwafer 32, patterning the metal hard mask, using the patterned metal hardmask to etch an underlying dielectric layer to form trenches or viaopenings, and removing the hard mask using wet-clean circulation system10. In subsequent processes, a seed layer (not shown) is deposited onwafer 32, followed by a plating process to fill the trenches and viasopenings with a metallic material such as copper. A Chemical MechanicalPolish (CMP) is then performed. The resulting metallic material in thetrenches and the via openings form metal lines and vias, respectively.

The metal ions in metal hard mask is dissolved in wet-clean chemical18B, and the resulting wet-clean chemical 18 including the metal ions isreferred to as wet-clean chemical 18C. Wet-clean chemical 18C iscollected from process chamber 30. If it is determined that the qualityof wet-clean chemical 18C is high enough, and wet-clean chemical 18C isre-usable, it is sent to pump 12, and then pumped back to storage 16. Ifit is determined that wet-clean chemical 18C cannot be reused anymore,wet-clean chemical 18C is drained (represented by arrow 34) as a wastechemical. As shown in FIG. 1, storage 16, filter 20, monitor 26, heater28, and process chamber 30 are connected as a loop.

Since wet-clean chemical 18C is eventually drained, fresh wet-cleanchemical 18, which may be free from the metal ions, is replenished intowet-clean circulation system 10 from time to time in order to maintainan adequate amount of wet-clean chemical 18.

When it is determined that porous exchanger 24 (FIG. 2) has trappedenough metal ions to a degree that its metal-trapping ability needs tobe improved, porous exchanger 24 is rejuvenized. The determination maybe achieved by monitoring the metal ions in wet-clean chemical 18B thatcomes out of porous exchanger 24. Alternatively, porous exchanger 24 maybe rejuvenized periodically. For example, if the metal ion concentrationin wet-clean chemical 18B is higher than a threshold level, then porousexchanger 24 needs to be rejuvenized. FIG. 3 illustrates an exemplaryprocess for rejuvenizing porous exchanger 24. First, the introduction ofwet-clean chemical 18A into metal-ion absorber 22 is stopped.Rejuvenizing chemical 36 is then introduced into porous exchanger 24 toremove metal ions from porous exchanger 24. During the rejuvenizingprocess, rejuvenizing chemical 36 may pass through the pores in porousexchanger 24, so that rejuvenizing chemical 36 is in contact with thepolymer and the trapped metal ions.

The available rejuvenizing chemicals 36 include solvents and gases. Forexample, the exemplary rejuvenizing chemicals 36 include a base or anacid, and porous exchanger 24 is flushed using the exemplaryrejuvenizing chemicals 36. Alternatively, the rejuvenizing process mayinclude a thermal desorption, wherein a hot solvent is used to removethe metal ions. In some embodiments, the hot solvent includes sulfuricacid, phosphate acid, sodium hydroxide, or the like. In yet alternativeembodiments, hydrogen (H₂) may be used to remove the metal ions from thepolymer in porous exchanger 24. In some embodiments, after therejuvenizing process, the polymer is restored back to the form R—H,R—OH, or the like, wherein the metal ions (M²⁺, M³⁺, and/or M⁴⁺, referto Equations 1 through 3) that are connected to the functional groups Rin the polymers are replaced by hydrogen (H) or hydroxide (OH). Themetal ions are removed from metal-ion absorber 22 along with the usedrejuvenizing chemicals 36, which is denoted as 38 in FIG. 3.

The rejuvenizing process may be performed inside metal-ion absorber 22.Alternatively, porous exchanger 24 is taken outside of metal-ionabsorber 22 to perform the rejuvenizing process. After the rejuvenizingprocess, the flow of wet-clean chemical 18 is restored, and wet-cleancirculation system 10 re-operates.

FIGS. 1 and 3 illustrate single-channel wet-clean circulation system 10in accordance with some embodiments. In alternative embodiments,wet-clean circulation system 10 include multiple channels, which may beinclude two channels, three channels, four channels, or more than fourchannels. The multi-channel wet-clean circulation system 10 may workunder a switch mode, wherein the multiple channels may be switched onand off, so that one of the channels is always turned on to trap themetal ions. FIGS. 4 and 5 illustrate the operation of an exemplaryswitch-mode dual-channel wet-clean circulation system 10. Referring toFIG. 4, two channels are connected to filter 20 through switch 40. Thefirst channel includes metal-ion absorber 22A and the correspondingpipes. The second channel includes metal-ion absorber 22B and thecorresponding pipes. Each of metal-ion absorbers 22A and 22B may have astructure essentially the same as metal-ion absorber 22 in FIG. 1.Switch 40 is configured to turn on one of the first channel 42 andsecond channel 44, so that the corresponding metal-ion absorber 22A or22B receives wet-clean chemical 18. At the same time, the other channelis turned off by switch 40, as shown by the “x” marks. For example, inFIG. 4, the first channel 42 is turned on, and hence metal-ion absorber22A is used to trap the metal ions in wet-clean chemical 18A. The porousexchanger 24 in the second channel may be rejuvenized at this time byconducting rejuvenizing chemicals 36 into metal-ion absorber 22B. Theused rejuvenizing chemical 38 is also drained.

Referring to FIG. 5, the second channel 44 is turned on, and hencemetal-ion absorber 22B is used to trap the metal ions in wet-cleanchemical 18A. The first channel 42 is turned off, as shown by the “x”marks. The porous exchanger 24 in the first channel 42 is rejuvenized.Accordingly, by switching the multi-channels, there is always onechannel that is on-line for processing wet-clean chemical 18A. The downtime of the respective wet-clean circulation system 10 is minimized.

In the embodiments of the present disclosure, the metal ions in thewet-clean chemical are removed, and hence the lifetime of the wet-cleanchemical is extended. The loading of the wet-clean chemical is improved,and the wet clean process in accordance with the embodiments is morestable. Furthermore, the manufacturing cost of the respective integratedmanufacturing process is reduced due to the saving in the wet-cleanchemical. The chemical waste is also reduced.

In accordance with some embodiments, a method includes passing achemical solution through a metal-ion absorber, wherein metal ions inthe metal-ion absorber are trapped by the metal-ion absorber. Thechemical solution exiting out of the metal-ion absorber is then used toetch a metal-containing region, wherein the metal-containing regionincludes a metal that is of a same element type as the metal ions.

In accordance with other embodiments, a chemical solution is passedthrough a metal-ion absorber. The titanium ions in the chemical solutionare trapped by the metal-ion absorber when the chemical solution ispassed through the metal-ion absorber. A hard mask in a semiconductorwafer is etched using the chemical solution that flows out of themetal-ion absorber, wherein the hard mask comprises titanium. Thechemical solution is collected after the chemical solution is used toetch the hard mask. The chemical solution that is used to etch the hardmask is conducted back to the metal-ion absorber.

In accordance with yet other embodiments, an apparatus includes ametal-ion absorber configured to absorb metal ions in a chemicalsolution, and a process chamber connected to the metal-ion absorberthrough a pipe. The pipe is configured to conduct the chemical solutionfrom the metal-ion absorber to the process chamber. The process chamberis configured to perform an etching on a hard mask in a wafer. Aconduction path connects the process chamber back to the metal-ionabsorber, wherein the conduction path is configured to conduct thechemical solution back to the metal-ion absorber.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: using a wet-cleancirculation system to circulate a chemical solution, the wet-cleancirculation system comprising: a storage; a filter connected to thestorage; a metal ion absorber connected to the filter; a monitorconnected to the metal ion absorber; and a process chamber, wherein thestorage, the filter, the metal ion absorber, the monitor, and theprocess chamber are connected in series to allow the chemical solutionto circulate in the wet-clean circulation system; conducting thechemical solution through a first metal-ion exchanger in the metal ionabsorber to remove metal ions from the chemical solution; andrejuvenizing the first metal-ion exchanger.
 2. The method of claim 1further comprising reusing the first metal-ion exchanger that has beenrejuvenized to further perform metal ion exchange in the wet-cleancirculation system.
 3. The method of claim 1 further comprising:conducting the chemical solution through the filter; and monitoring anamount of metal ions in the chemical solution.
 4. The method of claim 3,wherein the rejuvenizing the first metal-ion exchanger is performed inresponse to a result of the monitoring the amount of metal ions.
 5. Themethod of claim 1, wherein the first metal-ion exchanger comprises: abase material with a plurality of pores in the base material, whereinthe plurality of pores is interconnected with each other to form aplurality of paths penetrating through the base material; and a polymercoated on inner surfaces of the plurality of pores, wherein the polymeris configured to trap metal ions in the chemical solution.
 6. The methodof claim 1, wherein the metal ion absorber comprises: a first channelcomprising the first metal-ion exchanger; and a second channelcomprising a second metal-ion exchanger, wherein each of the firstchannel and the second channel is configured to be turned on and offindividually.
 7. The method of claim 6 further comprising: switching offthe first channel to stop the first metal-ion exchanger from receivingthe chemical solution, wherein the rejuvenizing the first metal-ionexchanger is performed after the first channel is switched off; andswitching on the second channel to allow the second metal-ion exchangerto trap metal ions in the chemical solution.
 8. A method comprising:circulating a chemical solution in a wet-clean circulation system,wherein the wet-clean circulation system comprises: a storage configuredto store the chemical solution; a filter configured to filter particlesin the chemical solution; a metal ion absorber configured to absorbmetal ions in chemical solution; and a monitor configured to monitor thechemical solution; etching a metal-containing feature in a wafer usingthe chemical solution; removing metal ions from the chemical solutionthat has been used to generate a cleaned chemical solution; and usingthe cleaned chemical solution to etch a second wafer.
 9. The method ofclaim 8 further comprising replenishing unused chemical solution to mixwith the chemical solution that has been used for etching themetal-containing feature.
 10. The method of claim 9, wherein theremoving the metal ions is performed on the chemical solution thatcomprises the unused chemical solution mixed with the chemical solutionthat has been used for etching the metal-containing feature.
 11. Themethod of claim 8, wherein the wet-clean circulation system isconfigured to monitor an amount of metal ions in the chemical solutionusing the monitor, and rejuvenize a metal-ion exchanger in the metal ionabsorber.
 12. The method of claim 8, wherein the metal ion absorbercomprises a metal-ion exchanger, and the metal-ion exchanger comprises:a porous base material; and a polymer coated on surfaces of the porousbase material, wherein the polymer is coated into pores of the porousbase material.
 13. The method of claim 8, wherein the metal ion absorbercomprises: a first channel comprising a first metal-ion exchanger; and asecond channel parallel to the first channel, the second channelcomprising a second metal-ion exchanger, wherein both the first channeland the second channel are configured to conduct the chemical solution.14. The method of claim 13 further comprising: switching off the firstchannel to stop the first metal-ion exchanger from receiving thechemical solution; and switching on the second channel to allow thesecond metal-ion exchanger to trap metal ions in the chemical solution.15. The method of claim 11 further comprising using the rejuvenizedmetal-ion exchanger to further remove metal ions from chemicalsolutions.
 16. The method of claim 8, wherein the etching is performedin a process chamber comprising a drain and a conducting path connectingthe process chamber to the storage, and the wet-clean circulation systemis configured to: determining a quality of the chemical solutioncollected from the process chamber; in response to the quality to behigher than a pre-determined quality, conducting the chemical solutionback to the storage; and in response to the quality to be lower than thepre-determined quality, drain the chemical solution to the drain.
 17. Amethod comprising: etching a first wafer using a chemical solution in aprocess chamber; directing the chemical solution out of the processchamber; mixing the chemical solution directed out of the processchamber with a fresh chemical solution to generate a mixed chemicalsolution; and removing metal ions in the mixed chemical solution using awet-clean circulation system, wherein the wet-clean circulation systemcomprises: a metal ion absorber configured to absorb the metal ions inthe chemical solution; a monitor connected to an outlet of the metal ionabsorber, wherein the monitor is configured to monitor an amount ofmetal ions in the chemical solution; and the process chamber, whereinthe process chamber is configured to receive the chemical solution outof the monitor.
 18. The method of claim 17, wherein the wet-cleancirculation system comprises a closed loop, with the metal ion absorber,the monitor, and the process chamber in the closed loop.
 19. The methodof claim 17 further comprising: in response to a result of monitoringthe amount of metal ions, rejuvenizing a metal ion exchanger in themetal ion absorber; and reusing the metal ion exchanger that has berejuvenized.
 20. The method of claim 17, wherein the metal ion absorbercomprises: a first channel comprising a first metal-ion exchanger; and asecond channel comprising a second metal-ion exchanger, wherein each ofthe first metal-ion exchanger and the second metal-ion exchanger isconfigured to absorb ions when the other one of the first metal-ionexchanger and the second metal-ion exchanger is being rejuvenized.